US2287671A - Tubular melting furnace - Google Patents

Description

J1me 1942- P. DUNSHEATH ET AL 2,237,671

TUBULAR MELTING FURNACE Filed Nov. 25, 1940 3 Sheets-Sheet l gaa AVE/VTOI? 5y m m w v A 7 TOR/V5 Y Q June 23, 1942. p DUNSHEATH HAL 2,287,671

TUBULAR MELTING FURNACE Filed Nov. 25, 1940 3 Sheets-Sheet 2 7' A 7 IVVF/V 0 zzat ATTORNEY ATTO/P Vf P. DUNSHEATH ETAL T LAR MELTING FURNACE Filed Nov. 25, 1940 June 23, 1942.

v mi Patented June 23, 1942 UNITED STATES PATENT OFFICE TUBULAR MELTING FURNACE Application November 25, 1940, Serial No. 367,057 In Great Britain January 25, 1939 Claims.

This invention is concerned with inclined tubular furnaces for the melting of metal ingots, such as ingots of lead or lead alloys. Furnaces of this kind comprise a relatively long melting chamber of a cross-section appropriate to that of the ingots to be melted which are introduced through a charging aperture in the upper end of the chamber at suitable intervals of time. The chamber has a smooth bottom wall designed to allow the ingots to slide down the furnace. In some cases a spring buffer is provided which engages with the ingot and brings it to rest in the desired position, where it is melted by heat transferred to it, both directly and through the surrounding molten metal, from the walls of the furnace. The latter are generally of metal, usually iron or steel, and heated externally by gas jets although proposals have been made to heat the furnace electrically either by electric resistance heating or by alternating current induction heating. By the present invention we provide an improved electrically heated melting furnace of this type. The improved furnace comprises a melting chamber having a central portion with a relatively thick bot tom wall in which are a number of transversely extending cylindrical recesses in some or all of which are fitted one or more electric heaters of corresponding form, and means are provided for arresting and retaining an ingot inserted in the furnace in this central portion until melted. The

heaters are arranged to be a close fit in the recesses to reduce the thermal resistance between the outer wall of the heater and the furnace wall as much as possible. For this reason the recesses will usually be of circular cross-section. Generally they will extend at right angles to the length of the furnace, preferably from side to side of the bottom wall. Where the upper inclined wall of this central portion of the furnace is flat, it may also be of relatively thick metal and be fitted with heaters in a similar manner to the bottom wall underlying it.

In order to provide for the accommodation of more or larger heaters in the central portion of the furnace, this portion or a part thereof may be of increased width as compared with that of the remainder of the furnace, the additional width being located wholly to one side or partly to one side and partly to the other side of the longitudinal axis of the furnace. In this case means are preferably provided to guide the ingot past the lateral pocket or pockets so formed. This may take the form of a ported vertical wall dividing the central part of the chamber from the pocket.

The heaters are preferably arranged in parallel in groups by connecting to bus-bars disposed on one or both sides of the furnace and thermostatically controlled.

To enable the invention to be more fully understood an example of a furnace constructed in accordance with the invention will now be described with the aid of the accompanying drawings, wherein:

Figures 1 and 1A are complementary views constituting a longitudinal section through the melting chamber of the furnace, Figure 1A illustrating the upper end of the structure of Figure 1;

Figure 2 is a view of the underside of the melting chamber, showing the disposition of the heaters in the bottom wall;

Figure 3 is a section of the furnace on the line IIIIII in Figure 1; and

Figure 4 is a cross-section, on the line IVIV of Figure 1 and on an enlarged scale, of the melting chamber fitted with a heat insulating casing.

As will be observed, the furnace comprises an inclined melting chamber I of rectangular crosssection which is somewhat greater in width than in height and has a length of about twelve times its width. The chamber is built up of welded steel plate and comprises a top wall 2 and a bottom wall 3 and a pair of side walls 4, 5. These walls are about half an inch thick except in a central portion of the chamber, which extends from a point about one quarter of the length from the lower end of .the chamber to a point about three quarters of the length from that end, in which the top and bottom walls are formed of steel plate two inches thick. These thick plates, 6, l, are

each of T-form and extend laterally beyond the side wall 4 for a distance somewhat greater than the width of the melting chamber. The space between the edges of these projecting parts of the plates 6 and l is closed by a side wall 8 and upper and lower end walls 9 and Ill, respectively, to provide a lateral chamber II which is placed in communication with the main chamber by a port l2 in the side wall 4, extending substantially the length of the lateral chamber. A series of reamed circular holes l3 are provided in the thick plates 6 and I, all but two of which in the bottom plate and all of which in the top plate extend right through from edge to edge of the plates. The two blind holes, designated l3a, house thermostats M. The remaining holes house electric heaters l5 of the type generally termed immersion heaters. With the exception of those designated I3b, the long holes in the part of increased Width each house two heaters which are separated by a short distance piece it. The holes 13b and the shorter holes i3 each house only a single heater, the heaters in the holes I31) being located below the main melting chamber and the remaining part of each of these holes being filled by a blank. The heaters are retained in position by plugs ll housed in metal support tubes [8 which enter a counterbore at each end of each hole and are secured thereto by welding. The leads it from each heater are brought out through suitable holes in the adjacent plug ll, the holes in the plug at the other end of the hole 13 being blocked up if not required. It will be apparent that the furnace shown can accommodate between fifty and sixty heaters. These are preferably of 660 watts and suffice for a furnace having a normal melting capacity of 1 ton of lead' per hour. Where a three phase A. C. supply is used the number of heaters is preferably a multiple of three so that the load may be equally distributed over the three phases. For instance, the bottom wall of the main melting chamber I may be fitted with eighteen heaters (one of the holes i3, e. g. the lowermost, being left empty), the top wall with eighteen and the top and bottom walls of the lateral chamber ll each with nine heaters.

The thermostat Hi that is located near the lower end of the central portion of the melting chamber serves to control the temperature thereof and the other operates as a safety device to cut off the supply should the upper heaters become too hot due to an abnormal fall in the level of the molten metal from the normal level which will generally be arranged to be just above the 5 uppermost heater.

The efficiency of the furnace as so far described with reference to the drawings is increased somewhat by the building of an auxiliary chamber over the part of the central por tion that is of increased width. This auxiliary chamber comprises vertical walls 2!, a fioor constituted by the top wall 6 of the melting chamber and a cover (not shown). It is placed in communication with the main melting chamber I and the lateral chamber II by ports. Preferably two ports, 22 and 23, are provided, extending across the greater part of the width of the floor of the auxiliary chamber, one near the lower edge of the floor and the other near the upper edge, and both passing in a vertical direction through the plate 6. When an ingot Z4 is fed in from a lock chamber (not shown) into the melting chamber it slides down the melting chamber until it is arrested, in the position indicated, by the spring buffer 25 comprising a pair of tubular members 33 and 34, the upper 33 of which is telescoped in the lower 34 and supported at its bottom end by a helical spring 35' positioned in the tube 34. Molten metal flows down these tubular members and out through the opening 35 in the side Wall of the chamber, communication between the interior and exterior of the tube 34 being provided by an aperture in the wall thereof coincident with the aperture 36 in the wall of the chamber. The movement of the ingot tends to swill any dross that may be present on the surface of the metal in the melting chamber into the auxiliary chamber 20, from which it may be removed over the weir 2% through the opening 21 by mechanical means. The auxiliary chamber may also accommodate a float or a level-indicating electrode.

Naturally the furnace is encased in heat insulating material to reduce radiation from the outer walls thereof, but for the sake of simplicity this has been omitted from Figures 1, 2 and 3. However, Figure 4 shows clearly the form which this insulation may take. The walls of the main melting chamber are directly surrounded by heat insulation 28 applied in a plastic state. This in turn is enclosed in a casing built up of magnesia slabs 29 and the whole is encased in a sheet metal casing 30 carried by brackets 3i welded to the chamber walls. In addition radiation losses from the lower part of the furnace may be compensated for by heat supplied by electrical resistance heaters (not shown) clamped against the outside of the furnace walls. Built on the sides of the casing 32! is bus-bar chamber 32 in which the leads I9 are connected. A second and smaller bus-bar chamber will be located on the outside wall of the lateral chamber l'l. This is not shown in the drawings.

What we claim as our invention is:

1. In an electrically heated inclined tubular furnace for the melting of metal ingots, a long melting chamber with a lateral pocket resulting in a central portion of the chamber being of greater width than the end portions, a plurality of cylindrical electric heaters fitted in transversely extending recesses of corresponding form in the bottom wall of said central portion of reater width, and means for guiding an ingot fed into the chamber from the upper end, past the lateral pocket in the central portion and means for arresting the downward movement of the ingot and retaining it on the electrically heated bottom wall of said central portion and opposite said lateral pocket.

2. In an electrically heated inclined tubular furnace for the melting of metal ingots, a long melting chamber, a lateral chamber disposed adjacent a central portion of the melting chamber and placed in communication therewith through a port in the side wall of the melting chamber, and a plurality of cylindrical electric heaters fitted in transversely extending recesses of corresponding form in the bottom walls of the central portion and of the lateral chamber and means for arresting the downward movement of an ingot fed into the melting chamber and retaining said ingot on the electrically heated bottom Wall of said central portion and opposite the port in said side wall.

3. In an electrically heated inclined tubular melting furnace for the melting of metal ingots, a long melting chamber having a central and two end portions, a pair of thick metal plates which constitute the top and bottom walls of said central portion and are each furnished with a series of cylindrical recesses extending transversely from an edge of the plate, a plurality of cylindrical electric heaters each fitted in one of said recesses, and means for arresting the downward movement of an ingot fed into the furnace and retaining it between the electrically heated upper and lower plates until melted, said means comprising a pair of telescopic tubular members in the lower end portion of the melting chamber, the inner of which is supported at its lower end by a helical spring and carries at its upper end, which extends to the lower end of the central portion of the chamber, a bridge piece adapted to engage the lower end of an ingot.

4. In an electrically heated inclined tubular furnace for the melting of metal ingots, a long melting chamber, a group of tubular electric heaters housed in transversely extending recesses in the relatively thick bottom wall of the central portion of said chamber, means for retaining an inserted ingot on the electrically heated bottom wall of the central portion of said chamber until melted, means comprising a thermostat housed in the bottom wall of the central portion of the melting chamber near the lower end thereof for regulating the supply of current to the heaters of said group, whereby to control the temperature of the molten metal in the central portion, and means comprising a thermostat housed in the bottom Wall of the central portion of the melting chamber near the upper end thereof for cutting off the current supply to the said heaters of said group controlled by said regulating means when the upper heaters thereof become overheated due to an abnormal fall in the level of molten metal in the said melting chamber.

5. In an electrically heated inclined tubular furnace for the melting of metal ingots, a long melting chamber having a central and two end portions, said central portion having a relatively thick bottom wall, in which are a plurality of cylindrical recesses extending transversely of the melting chamber, a plurality of cylindrical electric heaters, each fitting in one of said recesses, means for arresting the downward movement of an ingot fed into the furnace and retaining it on the electrically heated central portion, and heat storage means for preventing excessive temperature variations and solidification of molten metal in the central portion of the melting chamber by an ingot fed into the furnace, said heat storage means comprising an electrically heated chamber disposed laterally of the central portion of the melting chamber and having one wall thereof formed by a part of the adjacent side wall of the melting chamber, the part of the wall common to both chambers being ported.

PERCY DUNSHEATH. FRANCIS TADMAN GRIFFITHS.

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